Identification of Prolactin Synthesis at Early Differentiation Stage of T Cells in the Thymus

Abstract

Ectopic gene expression of prolactin (PRL) has been reported in different tissues among several species. Recently, lymphocytes have also been shown to produce PRL, which is considered to be involved in the immunoregulatory system. However, when and where PRL synthesis occurs in lymphocytes remain unknown. In the present study, we attempted to examine the existence of PRL producing cells in the mouse thymus and spleen of immune tissues. We performed double fluorescence immunohistochemistry (DFIH) for mouse PRL (mPRL) and mouse CD4 that was specifically produced in T cells, and for mPRL and mouse CD25 or CD44, which specify the CD4+ precursor cells in the early stage of T cell differentiation in the thymus. Similarly, we performed DFIH for mPRL and mouse IL-4 or IFN-γ which are specifically produced in helper T cells of the mouse spleen. The immunoreactive substance for mPRL was co-localized in some CD4 or CD44 immunopositive cells in the thymus and some IL-4 or IFN-γ producing cells in the spleen. In conclusion, we found that mPRL is synthesized at the early stage of T cell differentiation.